This invention provides a combination of anti-wear agents and polymers to form diesel engine lubricants with unique boundary films in the presence of abrasive contaminants.
In order to prevent wear, lubricants may form sacrificial films on rubbing surfaces. Zinc dialkyl dithiophosphates (ZDDP) are the most common anti-wear agents used in lubricants that act in this manner. However, in modern diesel engines and in off-road applications contaminants are usually present in the lubricant and can cause abrasive wear. The sacrificial films formed by lubricant additives must therefore be tenacious. We have discovered that there are specific combinations of ZDDP and polymers that can work synergistically to form tenacious boundary films. Zinc dialkyl dithiophosphates are well known in the art. For example, see U.S. Pat. Nos. 4,904,401; 4,957,649 and 6,114,288, which are incorporated herein by reference in their entirety.
This invention is a lubricating oil composition comprising a major amount of an oil of lubricating viscosity and a minor amount of a combination of at least one functionalized polymer, and at least one zinc dialkyl dithiophosphate (ZDDP), wherein the ZDDP is made from a mixture of primary alcohols or a mixture of primary and secondary alcohols, wherein the lubricating composition has a high boundary film result as measured by using a High Frequency Reciprocating Rig (HFRR), of greater than or equal to 15, preferably greater than 20, more preferably greater than 30, and most preferably greater than 60.
Preferably, the lubricating composition has a viscosity suitable for use in lubricating a diesel engine. Also, the preferred functionalized polymers are an amine-capped, grafted olefin copolymer or a copolymer of non-functionalized and functionalized methacrylate monomers. Preferably, the ZDDP is made from a mixture of primary alcohols or a mixture of primary and secondary alcohols.